Central heater

Central Heaters Room Heaters Wood Cracked heat exchanger Not enough air to burn fuel properly Defective/blocked flue Green or treated wood... 

Room Heaters Central Heaters Kerosene Improper adjustment Wrong fuel (not-K-1) Wrong wick or wick height Not enough air to bum fuel properly... 

A schematic of an Anter radial thermal conductivity measuring instrument using this principle is shown in Figure 9.2. A specimen in the form of an annular cylinder is placed to surround a central heater. Often the cylinder is made up of a series of stacked rings. Alternatively, a granulated or fibrous form of the specimen may be poured or placed between the central heater ( 1.2 cm OD) and a mullite outer casing ( 10.5 cm ID). 

Figure 9.2 Schematic of radial thermal conductivity apparatus. Specimen dimensions are 2.75 cm in radial thickness and 56 cm in length. Not shown are thermocouples placed axially along the central heater and voltage taps 5 cm apart. Inner and outer thermocouple junctions extend out radially, centered axially between the voltage taps.

The central heater is made up of a platinum heater assembly within an alumina or mullite sheath.1 Voltage taps symmetrically placed about the center allow determination of power per unit length dissipated radially past the inner and outer ther-... 

Mullite has the advantage that its lower thermal conductivity diminishes axial heat flow along the central heater more effectively. 

A tube furnace drawn over the mullite outer casing is used to heat the contents to a specified temperature, based on a furnace control thermocouple. At the same time, a constant ac voltage2 is applied across the central heater. The microprocessor waits until temperature fluctuations (within 0.1°C, over one minute) at any of the inside or outside thermocouples are eliminated.3 At that point, steady state conditions are assumed to exist. 

The heat flow dissipated by the central heater is then calculated by measurement of current and voltage (see section 9.3). The thermal conductivity is then computed based on the heat flow, temperature gradient, and known radial distances. The outer furnace then heats the contents to a higher (e.g. 100°C) temperature and the process repeats. The thermal conductivity of the specimen as a function of temperature is thus determined by a series of isothermal steps. 

The primary concern for accurate thermal conductivity measurements using this technique is to eliminate axial heat flow. As long as the central heater is long, its temperature near the central portion is uniform. Devoid of an axial temperature gradient, heat will strictly flow radially outward from the central... 

A new transduction technique that is being employed for inertial sensing is based on convective heat transfer. Temperature sensors around a central heater track convection as a function of acceleration input [68]. While this is not yet qualified for automotive production, it is a candidate for future devices. 

For power measurements, gamma thermometers depend upon heating of the instrument sensing area by fission and fission product gamma rays. A central heater cable along the assembly is provided for in situ calibration. 

Another type of capillary flow meter is shown in Fig. 1. A central heater (H) is wound about a thin-walled capDlaiy tube. Two resistive sensor elements are mounted on the capillary of the heater symmetrically, the upstream (SO and the downstream (S2), to monitor the temperature as depicted in the upper portion of Fig. 1. The difference in temperature between the two sensors... 

Calorimetric-type gas flow sensors analyze the temperature distribution built up in the environment around a central heater element [2]. Further explanation of its functionality is discussed in the next section. Using thermal electric circuits, thermal behavior of the sensor s stmcture is determined. A number of resistors and capacitors are used in the circuit to function as heat transfer agents. Flquation 11 is modeled for convective resistance and Eq. 12 for thermal capacitance where A is the heater area. The flow velocity can be obtained from Eq. 12. 

In between the elements is the central heater that heats up the gas as it passes by. This arrangement allows gas velocity to be measured. The thermal conduction, convection, and laminar flow condition of the gas are used for gas velocity determination. Figure 3 shows a typical output of this sensor. It depicts the simulated temperature values of the upstream and downstream resistors for different heater temperatures using nitrogen gas. It can be seen that the temperature difference between the upstream and downstream resistors increases... 

Fig. 2 Schematic of a one-dimensional calorimetric mass flow meter. The inhomogenous temperature distribution developing around the central heater characteristically represents the flow velocity [2]...

Calorimetric Sensors. The calorimetric type of gas flow sensors analyze the temperature distribution built up in the environment around a central heater element [2]. A photograph of a novel calorimetric sensor design is shown in Rg. 1, while Fig. 2 depicts the general idea behind the concept of calorimetric-type gas flow sensors. Figure 2 shows a single channel with two sensing elements, the tenper-ature resistors, attached upstream and downstream of the direction of flow. These elements confirm the direction of flow that can be in two possible directions. 

---